Co/CoO/Lotus Seedpod Nanoporous Carbon Composites Reduced from Co<sub>3</sub>O<sub>4</sub> for High-Performance Microwave Absorbers
Yupeng Qi, Yanting Qin, Hideo Kimura, Yukun Wang, Yaxin Yang, Cui Ni, Xueyu Yu, Chengguang Huang, Jingpei Tian, Ronghan Liu, Wei Du, Xiubo Xie
Abstract
To obtain microwave-absorbing materials with high absorptivity, broad bandwidth, and lightweight properties, Co 3 O 4 /lotus seedpod carbon (Co 3 O 4 /LSC) composites were reduced under a hydrogen pressure of 3 MPa. As the reduction temperature increases, the phases of the Co 3 O 4 /LSC composites change from Co 3 O 4 to CoO/Co. At 200 °C (named as the 3200 nanocomposite), partial Co 3 O 4 changes to CoO, the Co 3 O 4 completely transfers into CoO with a little Co detectable at 300 °C (3300 nanocomposite), and the concentration of Co increases more than that of the 3300 nanocomposite once temperature is raised to 400 °C (3400 nanocomposite). Moreover, the morphology of the Co 3 O 4 /LSC composites changes from irregular particles to a sintering state in the reduction process. When 3200, 3300, and 3400 nanocomposites are compared, the 3400 nanocomposite exhibits the highest permittivity and best microwave absorption performance: the 3400 nanocomposite exhibits a strong reflection loss of −60.63 dB (2.0 mm, 18.0 GHz) and an absorption bandwidth of 14.10 GHz (4.7 mm, 3.9–18.0 GHz). The hydrogenated LSC/Co 3 O 4 nanocomposite has a strong absorption capacity and wide effective bandwidth, is lightweight, and can be used as a high-performance biomass-based microwave-absorbing material.